For supplying electronic components within a motor vehicle, a generator, in particular an alternator, is generally used in addition to a vehicle battery. The generator, or alternator, is driven by a running motor as a secondary unit. The drive may be effected, for example, by means of a belt drive or directly via a crankshaft.
With a driven alternator, a current is provided by same, for example for charging the vehicle battery and for loads connected to an on-board network. The alternator transforms mechanical energy provided by the motor into electric energy, the mechanical power necessary being approximately proportional to the electrical power output. A non-regulated voltage provided by an alternator strongly varies with the rate of rotation of the motor and the load connected. Since an alternator should be able to build up the nominal voltage of the motor vehicle on-board network at a low motor speed already, it is generally oversized. To keep it from exceeding, as a consequence, an admissible final charging voltage of the vehicle battery in the event of a high rate of rotation, the voltage is generally limited to a maximum value by a regulator.
With three-phase current alternators, the electrically generated excitation field of the driven alternator rotor is influenced by an integrated circuit, i.e. by the electronic charging regulator, which is typically implemented on a side opposite the driving end. The regulator generally compares a rectified actual voltage at the output of the generator with a regulator-internal stable reference voltage and/or a setpoint voltage value, and adjusts the strength of the excitation field by means of a higher or lower level of generator excitation current flow through the rotor such that the actual voltage of the generator remains at least approximately constant independently of the load and speed. Conventionally, it is only the generator output voltage that is regulated in this context. However, the generator excitation current is generally not limited by the regulator.
What would also be desirable in addition to voltage regulation is a current limitation so that the mechanical load of the motor and gear box may be limited by the generator of a motor control device. It should be possible for the current limitation value to be set, for example, by the motor control device.